bpo-38870: Expose a function to unparse an ast object in the ast module (GH-17302)

Add ast.unparse() as a function in the ast module that can be used to unparse an
ast.AST object and produce a string with code that would produce an equivalent ast.AST
object when parsed.

Author: pablogsal

Doc/library/ast.rst

@@ -161,6 +161,19 @@ and classes for traversing abstract syntax trees:
       Added ``type_comments``, ``mode='func_type'`` and ``feature_version``.
 
 
+.. function:: unparse(ast_obj)
+
+   Unparse an :class:`ast.AST` object and generate a string with code
+   that would produce an equivalent :class:`ast.AST` object if parsed
+   back with :func:`ast.parse`.
+
+   .. warning::
+      The produced code string will not necesarily be equal to the original
+      code that generated the :class:`ast.AST` object.
+
+   .. versionadded:: 3.9
+
+
 .. function:: literal_eval(node_or_string)
 
    Safely evaluate an expression node or a string containing a Python literal or

Doc/whatsnew/3.9.rst

@@ -121,6 +121,11 @@ Added the *indent* option to :func:`~ast.dump` which allows it to produce a
 multiline indented output.
 (Contributed by Serhiy Storchaka in :issue:`37995`.)
 
+Added the :func:`ast.unparse` as a function in the :mod:`ast` module that can
+be used to unparse an :class:`ast.AST` object and produce a string with code
+that would produce an equivalent :class:`ast.AST` object when parsed.
+(Contributed by Pablo Galindo and Batuhan Taskaya in :issue:`38870`.)
+
 asyncio
 -------